1. Field:
This invention relates to snowmobile skis, and more particularly to steering skis for snowmobiles and similar vehicles.
2. State of the Art:
Steering a snowmobile is typically accomplished by a pair of steering skis pivotally attached to the front of the snowmobile. The steering skis glide over the surface of the snow and may be angularly turned from side-to-side in response to movement of a pair of handlebars grasped by a user. The snowmobile generally follows in the direction the skis are pointed.
Under most snow conditions, especially at high speeds, steering skis, when turned, have a tendency to slide sideways, i.e., "plow" forward over the surface of the snow rather than tracking as intended. The turning radius of the snowmobile thus becomes larger than anticipated, and may result in the user hitting something or losing control of the vehicle. If the sliding ski happens to suddenly "catch" in the snow, the momentum of the snowmobile can cause it to overturn and injure the rider. This situation is particularly hazardous under snowmobile-racing circumstances where the snowmobiles are driven at high speed. If a racer does not make a turn as anticipated, or suddenly loses control of his snowmobile, he can cause a high-speed accident, resulting in injury to the racers.
Various methods have been employed to lend increased predictability and control to snowmobile steering skis. One of the more common methods is inclusion of a longitudinal keel along the underside or running surface of the ski. The keel bites into the surface of the snow and enhances steering characteristics, particularly at high speeds.
U.S. Design Patent Des. 366,014 to Lindquist et al. dated Jan. 9, 1996 illustrates a conventional snowmobile ski having a straight central keel. The top surface of the ski has a continuous head along each edge and a plurality of very small, (thin in width and short in depth) straight, longitudinal ribs along the running (bottom) surface of the ski. The nature of a design patent is to illustrate aesthetic (non-functional) features. Thus, the upper beads and lower ribs appear to be non-functional in nature. Further, this design patent was filed about two years after Priority application Ser. No. 08/106,344 filed Aug. 12, 1993, identified herein above as a parent application to the instant application. That parent application illustrates and describes snowmobile skis having functional, multiple curved keels. The cited design patent shows, functionally, only a straight center keel of conventional shape and purpose.
A keel for a snowmobile, steering ski is disclosed in U.S. Pat. No. 3,632,126 to Shorrock. The keel disclosed in Shorrock has a straight running edge, and is adjustable to compensate for wear. U.S. Pat. No. 3,711,109 to Hofbauer discloses a snowmobile steering ski having a very short, curved keel resiliently attached to the ski runner. U.S. Pat. No. 3,643,978 to Westberg discloses a short curved flange which may be attached to the edge of a snowmobile ski, and which is intended to function similar to a keel.
U.S. Pat. Nos. 5,040,818 and 5,145,201 to Metheny illustrate snowmobile skies having a central keel with a planar lower surface as a part of a ski which has a laterally arched lower running surface.
Although the above inventions represent alternatives to a snowmobile ski without a keel, they are subject to several problems. The weight of both the snowmobile and the user is distributed evenly over the flat running surface of the skis in Shorrock, which places a portion of the weight at the ends of the straight keel. This makes the skis difficult to turn and lessens its usefulness. The bite of the keel into the surface of the snow is also distributed over a large area instead of concentrated in the most efficient location directly beneath the steering spindles. The short keel in Hofbauer tends to provide a concentration of weight beneath the steering spindles, but the amount of bite is reduced in soft snow due its short length. Also, because it is hinged, it tends to retract on hard snow pack or on ice, when a keel is very important. The short flange in Westberg also tends to concentrate weight beneath the steering spindles, but since it mounts on the edge of the ski, it actually exacerbates the problem of the ski "catching" in the snow during a turn, causing a loss of control even at moderate speeds. (The phenomenon is similar to the effect of a downhill skier catching a downhill edge during a turn.) Also, such short keels do not provide steering stability during straight runs and show a reduced steering ability in soft snow.
The inventions disclosed in Shorrock, Hofbauer and Westberg bring to light what has heretofore been a dilemma with respect to the design of snowmobile steering skis. Increased positive steering brought about by a long keel comes at the expense of ease of steering. Accordingly, a short keel makes the skis easier to steer, but reduces the amount of positive control. There is a need for a snowmobile steering ski that provides improved controllability and positive turning without a concomitant increase in steering difficulty.